Is a zebra without stripes still a zebra?

Yes, it is. Regardless of some minor mutation that affected its appearance, it still has the whole genome of the relevant species, it can mate with zebras and produce a zebra as a result. read more

Zoologically, a zebra without stripes is most likely to be an albino zebra. Albinism is a defect of melanin production that results in little or no color (pigment) in the skin, hair, and eyes. It results from inheritance of recessive gene alleles (genes) passed from both parents of an individual (though some rare forms are inherited from only one parent), and is known to affect all vertebrates, including humans. read more

So, a zebra without stripes looks more like a jackass than it does a horse. It would still be a zebra though, because zebras are defined by more than their stripes. They are defined by their entire being, including their DNA. read more